Harmless Watersnake or Venomous Water Moccasin?

There are many harmless watersnakes (genus Nerodia) that are
frequently confused with venomous Water Moccasins a.k.a. Cottonmouths (Agkistrodon
piscivorus). Sadly, harmless snakes are often killed out of fear
for the safety of family and pets. Most people, even those who
aren't afraid of snakes, would feel safer if they knew how to
rapidly identify snakes
near water as harmless or venomous. So how can you tell them
apart?

Harmless
Watersnake

Venomous
Water Moccasin

Usually found near water?

YES

YES

Body shape is...

SLENDER

HEAVY

Body dark, often with bands?

YES

YES

Rough-looking, keeled scales?

YES

YES

Head shape is...

SLENDER or FLATTENED

THICK, BLOCKY

Neck is...

NOT DISTINCT

NARROWER THAN HEAD

Dark facial band or eyestripe?

MAYBE

YES

Eye pupil type is...

ROUND

VERTICAL

Heat-sensing pits on face?

NO

YES

CAUTION!
-- With practice, you can learn to tell the difference
between watersnakes and Water Moccasins. Even non-venomous watersnakes
will bite, so the best policy for dealing with snakes is to "leave them be" to play their
important roles in our ecosystem.

Best ways
to tell watersnakes and Water Moccasins apart:

1.
BODY SIZE

THICK, HEAVY BODIES: Venomous Water Moccasins have bodies that are
VERY thick and heavy for their length, and short, thick tails. A harmless snake the same
length would be much more slender and would have a much longer,
thinner tail (see below).

The
body of this young, venomous Water Moccasin is very thick for its
length, and has a relatively short, thick tail. Notice that the head
is also thick and blocky. Older adults are often much darker --
almost solid black. (Note: this photo was sent to us by an Extension
client who needlessly killed the snake and asked that we confirm
that it was a venomous species. However, by killing the snake they
greatly increased their chances of being bitten--it is always best
to leave snakes alone!)

LONG, SLENDER BODIES: Non-venomous watersnakes (and
other harmless snakes) have bodies that are
more slender for their length, and longer tails.

This Brown Watersnake has a slender body
and has a relatively long, thin tail. Notice that the head is also
narrow.

**FLATTENED BODY: harmless watersnakes often flatten their
bodies and heads when they feel threatened, making themselves look much larger
and more menacing.

This Banded Watersnake feels threatened
and is
flattening its body and neck. However, for its length, the body of this snake is still more slender than the body of
a water moccasin, AND the tail is much longer and thinner.

2. HEAD AND NECK SIZE AND SHAPE

LARGE, BLOCKY HEADS: Venomous Water Moccasins have large,
blocky heads
and their necks are distinctly narrower than their heads.

This venomous Water Moccasin
has an obviously thick, (top to bottom) blocky head. (Note: this
photo was sent to us by an Extension client who needlessly killed
the snake and asked that we confirm that it was a venomous species.
However, by killing the snake they greatly increased their chances
of being bitten--it is always best to leave snakes alone!)

This venomous,
juvenile Water Moccasin also has a wide, blocky head, and a very obvious neck
that is narrower than the head. (Note: this photo was sent to
us by an Extension client who needlessly killed the snake and asked
that we confirm that it was a venomous species. However, by killing
the snake they greatly increased their chances of being bitten--it
is always best to leave snakes alone!)

SLENDER HEADS: Harmless watersnakes have slender heads that are
more narrow and less blocky, and they lack obvious necks.

This Banded
Watersnake has a slender, elongate head that blends into the body
smoothly, with no obvious neck.

This Green Watersnake
also has a slender head and no distinct
neck.

FLATTENED HEADS: Harmless watersnakes
often flatten their heads into a triangular shape when they feel
threatened, but their heads look flattened rather than thick and
blocky, and their necks are not distinctly narrower than their
heads.

This Banded
Watersnake feels threatened, so it has flattened its head and body
to appear more menacing. Harmless watersnakes often flatten their heads when they feel threatened, making their head look triangular--but
notice that the head looks flattened, not thick and blocky, and the neck
is almost as wide as the head.